|Re-entry and Landing
A spacecraft must re-enter Earth's atmosphere from a very high orbital speed and not burn up like a meteor. It must give up a lot of energy to slow down so that it can land safely.
After a ship finishes its mission, it prepares
for the bumpy ride down to Earth. It needs to slow down, so it turns
around to fire its engines in order to have a low enough speed to
fall down from orbit. The Space Shuttle lowers its speed by 200 miles
per hour before re-entering the Earth's atmosphere. Then it turns
around and faces down into the atmosphere at an angle of 30 degrees.
In the upper reaches of the atmosphere, the Space Shuttle travels
at around Mach 15 and still uses its thrusters for controlling. As
the atmosphere thickens, the Space Shuttle can use its aerodynamical
capabilities to move like an airplane. The Shuttle has a delta-wing
configuration that is optimized for traveling at high velocities while
maintaining control over the spacecraft. It has an elevator/aileron
on each wing that help it with rolling motion and moving up and down.
On its tail it has a rudder that controls left and right motion. The
underside of the Shuttle is coated with heat-resistant carbon-carbon
tiles that can sustain the heat of friction with the atmosphere without
burning up. The underside of the Shuttle can get as hot as 1650 degrees
Celsius during descent.
As the Shuttle nears its landing point, it travels in a series of
S-shaped turns that reduce its speed to about Mach 1. It is flown
by computer until it is about 40 kilometers from landing. At this
point, the commander takes control and flies the Shuttle in a wide
arc, lowering its speed to about 360 miles per hour. About 20 seconds
before touchdown, the pilot pulls up the nose of the Shuttle before
touching down on the runway at about 215 miles per hour. The Shuttle
takes several kilometers to stop, using the rudder and a drag parachute
as a brake.
Other spacecraft do not necessarily land on a runway. The Russian Soyuz capsule and the American Apollo module often land in the middle of the ocean, and sometimes on land. They use airbags and parachutes to slow the spacecraft before impact. There are rescue teams standing by to take the astronauts to safety.